The present invention relates to the field of radio receivers, and in particular to the field of motor vehicle radio receivers.
Radio receivers with so-called Autobest functionality have been know for some time. These receivers, which are mainly used for car radios, automatically seek another frequency of the same transmitter and tune to this frequency when the reception quality of a transmitter to which they are tuned falls below a certain limit. Even when a driver travels over large distances, which exceed the range of an individual broadcast station, he is thus able to continue listening to a transmitter without having to manually seek an alternative frequency when reception on the presently set frequency becomes unsatisfactory.
However, these receivers do not provide uninterrupted listening since the process of seeking a frequency of the same transmitter can take considerable time, within which the receiver repeatedly tunes to other frequencies and checks whether the transmitter received there is identical to the original one. If such an interruption automatically occurs during a transmission of radio reports, such as warnings of a traffic jam, this is extremely annoying for the listener even if the interruption takes only a few seeks.
In order for the transmitter with the best reception quality of multiple selectable transmitters to be tuned in, it is advantageous for the radio receiver to have available as much information as possible about the entire reception band. In the case of conventional Autobest receivers, operation is occasionally interrupted in the operating mode for this purpose in order, in the standby mode, to examine another frequency of the reception band to determine if, and at what quality level, a transmitter is receivable at this frequency, and what its identity is. The scanning of the entire FM frequency band for this purpose takes place over a time span of several seconds. An interruption of the audio signal output of this length tends to be unpleasant for a listener. For this reason, the conventional Autobest receiver only switches from the operating mode to the standby mode occasionally to determine if, and at what quality level, a transmitter is receivable at this frequency and what its identity is, and then records this information. It is self-evident that this approach to scanning the entire reception band takes several minutes.
To ensure that the Autobest functionality is quickly available after switching on the receiver, a known approach is to record the information collected about the frequency band and transmitters included in this band in a non-volatile memory so when the receiver is switched off, the stored information is immediately available when the receiver is switched on again.
This solution is not completely satisfactory for a number of reasons. First, non-volatile memories are relatively expensive, and for this reason the memory capacity is not provided that would be necessary to store information on all transmitters receivable in the frequency band. Only information on the most recently heard transmitter is stored. The result is that, when the user tunes in a new transmitter shortly after switching on the receiver, there is a considerable risk that information on the alternative frequencies for this new transmitter has not been stored, and this information must therefore be collected again. Since the receiver does not “know” in advance where to find alternative frequencies for the new transmitter, it must scan the entire reception band to find the alternative frequencies.
While this disadvantage may be eliminated by the generous use of non-volatile memory for the transmitter information, another disadvantage with the conventional approach can not be so easily avoided. If the receiver is switched off at a first location, then moved and switched on again at a second location, the stored transmitter information at the time it is switched on relates to the transmitter region at the first location, which may be completely different from that at the second location. In this case, the complete set of transmitter information must again be collected after the receiver is switched on before reception optimization is possible.
Therefore, there is a need for an improved technique for automatically determining alternative frequencies that transmitters are available on.